Adducts of 1,4-bis[(3-methacroyl-2-hydroxypropoxy)methyl] cyclohexane and derivatives thereof with isocyanates

ABSTRACT

Dimethacrylates are provided having the following chemical structure: &lt;IMAGE&gt;   where   &lt;IMAGE&gt;

BACKGROUND OF THE INVENTION

The present invention relates to a polymerizable compound, a polymerformed from this compound, a dental material containing this compound, amethod for polymerizing this compound in situ on teeth, and a toothcomprising a polymer of this compound.

In recent years, the use of polymer-based dental materials became veryprominent as they improved aesthetics and durability of restorations,faciliated application techniques and allowed great expansion of dentaltechniques in restorative, corrective and preventive applications.Especially important became filled restorative material, cements,bonding agents, fissure sealers and orthodontic adhesives based on thepolymerizable in situ aromatic and aliphatic methacrylates. The bestproperties in these materials have been obtained when the resin part ofthe composition is comprised of one or more of the following monomers:##STR5## i.e., 2,2-bis[4'(3"-methacroyl-2"-hydroxypropoxy)phenyl]propane(known in the industry as Bis-GMA), its adducts with variousalkyl-isocyanates, such as adducts described in the Waller U.S. Pat. No.3,629,187, the entire disclosure of which is hereby incorporated byreference and relied upon, and ##STR6## i.e.,2,2-bis[4'(2"-methacroylethoxy)phenyl]propane (known in the industry asEBA).

These high molecular weight monomers are usually diluted with lowermolecular weight polymethacrylates including dimethacrylates such asdi-, tri- or tetraethylene glycol dimethacrylate, 1,6-hexanedioldimethacrylate or trimethacrylates such as trimethylolpropanetrimethacrylate. Other methacrylate monomers known to be used in certainrestorative materials, cements, fissure sealers, bonding agents ororthodontic adhesives and claimed to improve mechanical, physical,clinical or aesthetic properties of materials are: ##STR7## i.e.,2-methacroylethyl-3-methacroyl-2-hydroxypropyl tetrahydro (or hexahydro)phthalate and ##STR8## i.e., 2,2-bis(4'-methacroylphenyl)propane (knownin the industry as BADM).

In an attempt to improve methacrylate resin based dental materials,research efforts have been concentrated mainly on reducing their watersorption, as related to susceptibility to hydrolysis and staining, onminimizing their polymerization shrinkage and on improving theirresistance to discoloration when exposed to sunlight.

These properties depend on the chemical structure of the monomer ormonomers used in the formulation and their purity. In the formulationscontaining (besides the resin binder) a solid phase in the form ofdispersed filler particles, the viscosity of the resin constitutesanother important factor. The lower the viscosity of the alternativemonomers that may be used in the formulation, other properties remainingsimilar or the same, the more filler may be incorporated in theformulation contributing to lower shrinkage, lower water sorption,better wear resistance and overall improved mechanical properties.

As it is recognized in the dental profession, the composite restorativesknown up to now were unsuitable in most instances for use in posteriorrestorations, mainly because of their unsatisfactory wear resistance.This is especially true for Class II restorations as exposed the most tostrong mastication forces. The typical properties of compositerestoratives made according to presently known techniques are givenbelow:

    ______________________________________                                        Water Sorption at 37° C.                                                                    0.7 mg/cm.sup.2                                          Compressive Strength 30,000-40,000 psi                                        Diametral Tensile Strength                                                                         3,480-4,600 psi*                                         Color Stability      Discoloration                                                                 perceptible with                                                              difficulty                                               Hardness (Barcol)    98                                                       Opacity/Translucency 0.35-0.55*                                               Filler/Resin ratio by Weight                                                                       3.2:1 to 4.2:1                                           ______________________________________                                         *Determined according to American Dental Association Specification No. 27     JADA Vol. 94, June, 1977.                                                

In addition to the above-mentioned Waller U.S. Pat. No. 3,629,187,various polymeric dental materials have been described in the followingU.S. Pat. Nos. 3,066,112 (Bowen); 3,179,623 (Bowen); 3,194,783 (Bowen);3,194,784 (Bowen); 3,539,533 (Lee II et al); 3,541,068 (Taylor);3,597,389 (Taylor); 3,721,644 (Stoffey et al); 3,730,947 (Stoffey etal); 3,751,399 (Lee, Jr. et al); 3,766,132 (Lee, Jr. et al); 3,774,305(Stoffey et al); 3,860,556 (Taylor); 3,862,920 (Foster et al); 3,926,906(Lee, II et al); 4,102,856 (Lee, Jr.); and 4,107,845 (Lee, Jr. et al).Further information on polymer based dental materials is given on pages501-508 and 515-517 of the Kirk-Othmer Encyclopedia of ChemicalTechnology, Third Edition, Volume 7 (1979). The entire disclosures ofthe patents and the Kirk-Othmer reference set forth in this paragraphare hereby incorporated by reference and relied upon.

An important improvement in clinical performance of polymer-based dentalrestoratives may be achieved and their scope of applications greatlyexpanded if their water sorption is lowered, mechanical strength andhardness improved and filler/resin ratio significantly raised.Accordingly, there is a need in the art to develop polymerizablecompounds which tend to overcome the shortcomings of the prior artpolymerizable compounds used in dental materials.

SUMMARY OF THE INVENTION

The present invention relates to a compound of the following formula:##STR9## where ##STR10## is a saturated, 6 membered, monocyclic,hydrocarbyl ring system; R₁, R₂ and R₃ are the same or different and arehydrogen or alkyl or alkoxy groups having 1 to 12 carbon atoms; and

R₄ and R₅ are the same or different and are hydrogen or groups of theformula: ##STR11## where R₆ is an aliphatic, aromatic or cycloaliphaticgroup having 1 to 14 carbon atoms, provided that at least one of thegroups R₄ and R₅ is a group of the formula: ##STR12##

Other aspects of this invention relate to a polymer formed from thiscompound, a dental material (e.g., particularly a composite restorativematerial) containing this compound, a method for polymerizing thiscompound in situ on teeth and a tooth comprising a polymer of thiscompound.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a dimethacrylate compound represented by thestructure: ##STR13## where ##STR14## is a saturated, 6 membered,monocyclic, hydrocarbyl ring system; R₁, R₂ and R₃ are the same ordifferent and are hydrogen or alkyl or alkoxy groups having 1 to 12carbon atoms; and

R₄ and R₅ are the same or different and are hydrogen or groups of theformula: ##STR15## where R₆ is an aliphatic, aromatic or cycloaliphaticgroup having 1 to 14 carbon atoms, provided that at least one of thegroups R₄ and R₅ is a group of the formula: ##STR16##

Dimethacrylate compounds of this formula are referred to hereinafter ascompounds of the present invention. A preferred compound of the presentinvention is represented by the above formula when R₁, R₂ and R₃ areeach hydrogen. It will be understood that structures given herein areintended to connote all possible sterioisomers and combinations thereof.

Although not wishing to be strictly limited to any particular means forforming the compounds of the present invention, it is noted that thesecompounds may be described as adducts of isocyanates with adducts ofmethacrylic acid with 1,4-bis(glycidoxymethyl)cyclohexane or ringsubstituted derivatives thereof. Thus, for example, methacrylic acid maybe reacted with a 1-4-bis(glycidoxymethyl)cyclohexane compound of theformula: ##STR17## where ##STR18## R₁, R₂ and R₃ are defined as above.Thus, the saturated 6 membered, monocyclic, hydrocarbyl ring representedby ##STR19## may be substituted by alkyl or alkoxy groups in up to 3positions. In this regard, alkyl or alkoxy groups may be substitutedonce in each of the 1, 2, 3, 4, 5 or 6 positions or even twice in eachof the 2, 3, 5 or 6 positions.

As mentioned previously, R₁, R₂ and R₃ may be alkyl or alkoxy groupshaving up to 12 carbon atoms. Such alkoxy groups may be represented bythe formula --OR₇ where R₇ defines the same class of alkyl substituentsas R₁, R₂ and R₃, i.e. alkyl groups having 1 to 12 carbon atoms.Preferably R₁, R₂, R₃ and R₇ have 1 to 4 carbon atoms. Examples of R₁,R₂, R₃ and R₇ include methyl, ethyl, n-propyl, isopropyl, n-butyl,isobutyl, tert.butyl, straight or branched chain pentyl, straight orbranched chain hexyl, straight or branched chain heptyl, straight orbranched chain octyl, straight or branched chain nonyl, straight orbranched decyl, straight or branched chain undecyl and straight orbranched chain dodecyl.

In forming the compounds of the present invention, the1,4-bis(glycidoxymethyl)cyclohexane compound may be reacted withmethacrylic acid at a temperature of about 85°-140° C. The reactionmixture may also contain a suitable electron donating catalyst such astriphenylphosphine and a polymerization inhibitor such as BHT. Moreinformation on reactions of carboxylic acids with epoxides may be foundin H. Frankel-Conrat and H. S. Olcott, J. Am. Chem. Soc. 66, 1420(1944).

The adduct of methacrylic acid and 1,4-bis(glycidoxymethyl)cyclohexaneor ring substituted derivatives thereof is a dihydroxy compound,represented by the following formula: ##STR20## This dihydroxy compoundmay then be converted to compounds of the present invention, e.g. mono-and/or dicarbamates of this dihydroxy compound, by reacting same withisocyanates of the formula

    R.sub.6 --N═C═O

where R₆ has the meaning defined above, i.e., an aliphatic, aromatic orcycloaliphatic group having 1 to 14 carbon atoms, e.g. hydrocarbongroups or haloaryl groups such as chloroaryl groups. Examples of groupsrepresented by R₆ include methyl, ethyl, n-butyl, isoamyl, n-amyl,hexyl, n-octyl, isooctyl, dodecyl, tetradecyl, phenyl, p-ethyl benzyl,p-tolyl, p-butylphenyl, xylyl, α-naphthyl, p-chlorophenyl, benzyl,cyclopentyl, m-chlorophenyl and cyclohexyl. A preferred grouprepresented by R₆ is n-butyl. As hydrocarbon groups for R₆ there can beused for example, alkyl, aryl, aralkyl and cycloalkyl.

Reaction of the above-mentioned dihydroxy compound intermediate withvarious proportions of isocyanates may produce dicarbamates,monocarbamates or mixtures thereof.

The dimethacrylates of the present invention may be combined with otherpolymerizable unsaturated materials, such as acrylic or methacrylicmonomers or prepolymers, and polymerized. Thus, the dimethacrylates ofthe present invention may be polymerized to form either homopolymers orcopolymers, e.g., containing at least 10% by weight of thesedimethacrylate moieties. Preferably, copolymers of the dimethacrylatesof the present invention may contain at least 40% by weight of thesedimethacrylate moieties, e.g., wherein the moieties of thedimethacrylates of the present invention represent the predominate unit,e.g., terpolymers containing 40% of units compounds of the presentinvention and 30% each of two other units. As used herein, the term"moiety" shall connote an entire repeating polymeric unit and not somelesser fragment thereof.

Polymers of the dimethacrylates of the present invention arecharacterized in that they may have a high degree of crosslinking.Accordingly, these dimethacrylates may be added to mono-functionalacrylic and methacrylic monomers and polymerized to form cross-linkedpolymers. Examples of these acrylic and methacrylic compounds includeacrylic and methacrylic acid and esters thereof with alcoholscontaining, e.g., 1 to 4 carbon atoms. Examples of such acrylic andmethacrylic esters include methylmethacrylate, ethylmethacrylate,butylmethacrylate, methylacrylate, ethylacrylate and butylacrylate.

Copolymers having an even higher degree of cross-linking may be producedby copolymerizing the dimethacrylates of the present invention withother polyfunctional acrylic ester or methacrylic ester monomers, i.e.,monomers containing two or more acrylic or methacrylic functionalities.One class of these polyfunctional monomers includes monomers which areused as diluents in dental materials. Such polyfunctional acrylic esteror methacrylic ester monomers include alkylene glycol diacrylates,alkylene glycol dimethacrylates, polyalkylene glycol diacrylates,polyalkylene glycol dimethacrylates, alkanetriol triacrylates andalkanetriol trimethacrylates, e.g., containing from 8 to 18 carbonatoms. Examples of such monomers include ethylene glycol dimethacrylate,di-, tri- or tetraethylene glycol dimethacrylate, 1,6-hexanedioldimethacrylate, the dimethacrylate formed by the reaction of methacrylicacid with butanediol, trimethylolpropane trimethacrylate and the acrylicesters corresponding to these methacrylates, e.g. ethylene glycoldiacrylate. As far as polyfunctional acrylates and methacrylates areconcerned, these monomers are characterized by relatively low molecularweight (e.g., 339 or less) and low viscosity. The above-mentionedpolyglycol dimethacrylates are further characterized by low surfacetension.

Another class of polyfunctional acrylates and methacrylates includes therelatively high molecular weight (e.g., 364 or more) acrylic ormethacrylic monomers used in dental compositions. Such polyfunctionalcompounds include, especially, dimethacrylates such as2,2-bis[4'(3"-methacroyl-2"-hydroxypropoxy)phenyl]propane (i.e.Bis-GMA), 2,2-bis[4'(2"-methacroylethoxy)phenyl]propane (i.e., EBA),2-methacroylethyl-3-methacroyl-2-hydroxypropyl tetrahydrophthalate,2-methacroylethyl-3-methacroyl-2-hydroxypropyl hexahydrophthalate and2,2-bis(4'-methacroylphenyl)propane (i.e. BADM). Further polyfunctionalmonomers containing up to four acrylic or methacrylic functionalitiesare described in the Stoffey et al U.S. Pat. No. 3,721,644, the entiredisclosure of which is hereby incorporated by reference and relied upon.

Accordingly, copolymers may be formed from polymerizable materialscomprising at least one dimethacrylate of the present invention and,e.g., at least 10% by weight of one or more of the copolymerizablematerials described herein.

Polymerization of the dimethacrylates of the present invention may beinitiated by known means for initiating the polymerization ofdimethacrylates such as heat, chemical means or electromagneticirradiation. Thus, in order to induce curing of dimethacrylates, afree-radical catalyst may be incorporated therein. Organic peroxideinitiators, such as methyl ethyl ketone peroxide, t-butyl peroctoate,iso-propyl percarbonate, cumene hydroperoxide, dicumyl peroxide, andespecially benzoyl peroxide, are preferred.

The ability of the initiator to cure dimethacrylates may be enhancedthrough the use of activators or accelerators. Thus, a peroxideinitiator can be activated with a tertiary aromatic amine such asN,N-dimethyl-p-toluidine or N,N-bis(2-hydroxyethyl)-p-toluidine.

The amount of free-radical catalyst may be selected according to thecuring rate desired. For instance, if a relatively slow curing rate isdesired, a minimum catalytically effective amount, such as 0.5% byweight based on the polymerizable components, may be selected. On theother hand, when faster rates of cure are desired, greater amounts offree-radical catalyst, such as 4.0% or more by weight based on thepolymerizable components, may be selected. Accordingly, the amount ofcatalyst may range from about 0.5 to about 4.0% by weight based upon theweight of the polymerizable components.

As with the free-radical catalyst, the amount of the activator selectedmay vary, e.g., from about 0.5 to about 4.0% by weight of thepolymerizable components, depending upon the desired curing rate.

Polymerization of the dimethacrylates of the present invention may alsobe initiated by ultraviolet or visible light using known light activatedpolymerization initiators such as benzoin, benzoin methyl ether, benziland other commercially available photoinitiators. For example, one mayselect from about 0.5% to about 5% by weight based on the polymerizablecomponents of a sensitizer capable of initiating polymerization whenexposed to UV light between about 3550A. to about 3720A.

The various components of a material containing a dimethacrylate of thepresent invention may be combined in any suitable manner. However, sincechemically initiated polymerization starts immediately upon admixture ofall three of (1) a methacrylate, (2) an initiator and (3) an activator,it is necessary to separate at least one of these components from theothers until immediately before polymerization of the methacrylate. Thisseparation may be achieved through the use of a two-package product,wherein various components of a material containing a dimethacrylate ofthe present invention are separately contained until the time ofpolymerization.

Therefore, the components of such a composition may be separated bymeans of a two-package product into two parts, one part containing thepolymerization initiator and the other part containing thepolymerization accelerator.

It is helpful to package polymerizable methacrylates with inhibitors,such as butylated hydroxytoluene (BHT) or hydroquinone methyl ether.Thus, BHT may be included in an amount from about 0.1 to about 0.3% byweight based on the polymerizable components to increase the storagestability of these polymerizable components.

Ultraviolet stabilizers such as 2-hydroxy-4-methoxybenzophenone (CyasorbUV-9, a tradename of American Cyanamide) may be included to enhance thestability of the polymerizable components as well as polymers resultingtherefrom. For example, from about 0.4 to about 1.6% by weight ofCyasorb UV-9 based on the weight of the polymerizable components may beused for this purpose.

In addition to polymerizable unsaturated material, inorganic orpolymeric fillers may also be added to the monomers of the presentinvention prior to polymerization of these monomers. Accordingly, theterm "polymer" as used herein may connote a polymeric matrix materialwhich binds together various fillers.

Up to about 6.5 parts of filler material per part of polymerizableunsaturated material may be included. Particular inorganic fillermaterials include silica materials (e.g., powdered quartz, bariumglasses, borosilicate glasses, SiO₂, fumed silica and lithium aluminumsilicate) and alumina materials (e.g., Al₂ O₃). These inorganic fillermaterials may be treated with coupling agents, such as[3-(methacroyl)propyl]trimethoxysilane, in order to assure the properincorporation of filler into the polymeric matrix of the cured product.Other materials such as pigments may also be included in polymerizablematerials comprising the dimethacrylates of the present invention.

It is noted that by varying the nature and proportions of curablecompositions comprising one or more dimethacrylates of the presentinvention, a variety of such curable compositions as well as a varietyof cured compositions resulting therefrom may be obtained. For example,curable compositions containing a relatively large amount of fillers,and relatively small amounts of low viscosity acrylic or methacrylicdiluents, as well as minimum amounts catalysts and activators, may havea thick, doughlike consistency and a slow curing rate permitting workingof the composition by molding and shaping before setting occurs. On theother hand, compositions containing little or no filler and relativelylarge amounts of low viscosity diluents, catalysts and accelerators maybe flowable and fast curing, permitting brush-on application wherelittle or no molding or shaping is required.

Polymerizable materials containing dimethacrylates of the presentinvention may now be described by way of examples of various dentalmaterials. In this regard, composite restorative materials are givenparticular emphasis.

COMPOSITE RESTORATIVE MATERIALS

Composite restorative materials, as the name implies, is a compositematerial of a polymerizable material and a suitable filler. Thesematerials are capable of curing in situ on teeth to restore a hardenedsurface thereto. These materials are generally applied as a fillingmaterial to prepare or drilled teeth. Accordingly, composite restorativematerials should be of a thick, workable consistency suitable forapplication to a prepared tooth and capable of being shaped or moldedthereon before setting occurs. Thus, composite restorative materials arerelatively slow curing.

The thick consistency of composite restorative materials, as well as thedesirable properties of the cured product formed from these materials,are largely a function of the relatively large amounts of fillermaterials employed therein. More particularly, composite restorativematerials may contain glass or ceramic fillers in excess of thepolymerizable material employed therein.

When the polymerizable material of the composite restorative containsone or more dimethacrylate monomers of the present invention, the weightratio of filler to polymerizable material may range about 1.5:1 to about6.5:1 and, most especially, from about 4:1 to about 6:1. Suitableceramic or glass fillers include silica materials, such as powderedquartz, barium glasses, borosilicate glasses, SiO₂ and lithium aluminumsilicate, and alumina materials, such as Al₂ O₃. Since compositerestorative materials must be capable of conforming to the confinedspace of prepared tooth and hardening therein to achieve restorativeproperties, the particle size of these fillers must be sufficientlysmall. Generally, the particle sizes of these fillers may range fromabout 1 to about 150 microns, preferably from about 1 to about 40microns. The average particle size of these fillers is preferably lessthan about 25 microns. Suitably, composite restorative materials maycontain a mixture of two or more fillers, such as a mixture of a ceramicfiller (e.g. powdered quartz) and glass filler (e.g., powdered glass).

According to techniques well known in the art, the fillers of compositerestorative materials may be treated with one or more organosilanecoupling agents. These coupling agents are also sometimes referred to asfinishing or keying agents and include materials such as[3-(methacroyl)propyl]trimethoxysilane. A sufficient coupling amount ofsuch coupling agent may be a small amount such as from about 0.5 toabout 1.0 part of coupling agent per 100 parts of filler. Methods fortreating fillers with coupling agents are described, for example, inU.S. Pat. No. 3,066,112 (Bowen), wherein an aqueous solution oftris(2-methoxyethoxy)vinyl silane is catalyzed with sodium hydroxide togive a pH of 9.3 to 9.8, and the filler is treated with this solution,for example, one-half percent of silane per weight of fused quartz. Aslurry so formed is dried at about 125° C. and cooled. Another techniquefor treating filler with a coupling agent is described in the passageextending from column 3, line 40 to column 4, line 4 of U.S. Pat. No.3,862,920 (Foster et al).

As indicated previously, the filler, rather than polymerizable material,constitutes a major portion of the composite restorative material.Perhaps for this reason the polymerizable material in compositerestoratives is sometimes referred to as a "binder".

The polymerizable materials for forming a composite restorative materialmay contain at least two monomeric components, termed herein a firstmonomer and a second monomer. This first monomer is at least onedimethacrylate monomer according to the present invention, and thesecond monomer is at least one relatively low molecular weight diluentmonomer which, among other purposes, serves to reduce the overallviscosity of the composite restorative materials.

The first monomer of the polymerizable material may be present in anamount of from about 20 to about 90% by weight, preferably from about 30to about 80% by weight, of the polymerizable material. The secondmonomer may be present in an amount from about 10 to about 80%,preferably from about 20 to about 30% by weight, of the polymerizablematerial.

As a second monomer, an acrylic or methacrylic diluent, which is usedfor this purpose in dental materials, may be selected. Moreparticularly, this diluent may be a di- or trimethacrylate having from10 to 18 carbon atoms. Diluents falling within this class of compoundsinclude relatively low molecular weight (e.g., 339 or less) alkyleneglycol dimethacrylates, polyalkylene glycol dimethacrylates andalkanetriol trimethacrylates. Particular examples of such diluentsinclude di-, tri- or tetraethylene glycol dimethacrylate, 1,6-hexanedioldimethacrylate, and trimethylolpropane trimethacrylate. Triethyleneglycol dimethacrylate is a preferred diluent.

The polymerizable material of composite restoratives may also contain atleast one third monomer. This third monomer may be a relatively highmolecular weight (e.g., 364 or more) polyfunctional acrylic ormethacrylic monomer used in dental compositions. Such polyfunctionalcompounds include dimethacrylates such as2,2-bis[4'(3"-methacroyl-2"-hydroxypropoxy)phenyl]propane (i.e.Bis-GMA), 2,2-bis[4'(2"-methacroylethoxy)phenyl]propane (i.e., EBA),2-methacroylethyl-3-methoacroyl-2-hydroxypropyl tetrahydrophthalate,2-methacroylethyl-3-methacroyl-2-hydroxypropyl hexahydrohthalate and2,2-bis(4'-methacroylphenyl)propane (i.e. BADM).

Although the third monomer constitutes a different class of materialsthan the first monomer, the first monomer and third monomer servesimilar functions. Therefore, the third monomer may be used as areplacement for a portion of the first monomer, provided that thepolymerizable material contains at least 20% by weight of the firstmonomer. This third monomer may be used in quantities close to thequantities of first monomer. For example, the weight ratio of the firstmonomer to the third monomer may range from about 3:5 to about 5:3.Accordingly, when the first monomer is present in an amount ranging fromabout 30 to about 50% by weight of the polymerizable material, the thirdmonomer may also be present in an amount ranging from about 30 to about50% by weight of the polymerizable material. Preferably, however, theweight percent of the first monomer is greater or equal to the weightpercent of the third monomer.

In describing various composite restorative compositions, mention hasbeen made of various specific compounds, such as triethylene glycoltrimethacrylate and Bis-GMA, which fall into classes of compoundsreferred to as a second monomer or third monomer. However, it will beunderstood that the polymerizable material of the composite restorativematerial may contain further compounds which may fall within thesecategories of second or third monomers and/or may even fall in someseparate and distinct category. For example, the polymerizable materialmay contain a small amount of methacrylic acid. However, due to theobjectionable odor and properties of methacrylic acid, this monomershould not be present in quantities in excess of about 2% by weight(e.g., between about 1 and 2% by weight of the polymerizable material).

Composite restorative compositions may be cured by any suitable means, achemically initiated system being preferred. This initiating systeminvolves the use of a catalyst and an accelerator. Peroxide catalystssuch as benzoyl peroxide and tertiary amine accelerators such asN,N-bis(2-hydroxyethyl)-p-toluidine are preferred. The amounts ofcatalyst and accelerator may each be from about 0.5 to about 2.0% byweight of the polymerizable materials.

Desirably, initial curing of the composite restorative material shouldtake place in about 1 to about 2 minutes upon admixture of thecomponents thereof in order to permit adequate mixing and manipulationof these components outside the mouth prior to application to a preparedtooth. However, final curing is desirably delayed for 4 to 6 minutesfrom the initial contacting of restorative components in order to permitproper molding and shaping inside the mouth. It is noted that templatestructures are sometimes used in this molding process. Compositerestorative materials having such curing characteristics may enable adentist to perform a complete restoration of a prepared tooth withinabout ten minutes, including grinding and polishing the restorativematerial after final setting.

Composite restorative materials may be packaged in any suitable manner.Preferably, a two-package system is used wherein each package containsfiller and polymerizable material in roughly equal amounts, one packagecontaining the catalyst and the other package containing theaccelerator. However, other systems are also possible. For example,according to another two-package system, one package may contain bothfiller and catalyst and the other package may contain polymerizablematerial and accelerator. Another system involves packaging togethereach of the components excluding the catalyst component. When thissystem is used, polymerization can be initiated by introducing catalystdropwise from a stock solution thereof. Such a stock solution isdescribed in the Taylor U.S. Pat. No. 3,541,068 (Note particularlycolumn 6, lines 23-50).

Whatever packaging system is used, it is helpful to packagepolymerizable materials with one or more polymerization inhibitors suchas BHT in order to enhance storage life. Also, shelf life of componentscontaining accelerators may be improved by removing traces of peroxidesfrom these components with a reducing agent.

Cured composite restoratives containing at least one monomer accordingto the present invention have desirable properties and may be capable ofholding up under strong mastication forces. For instance, thesematerials may have a water sorption at 37° C. of 0.5 mg/cm² or less(preferably 0.42 mg/cm² or less), a compressive strength of 40,000 psior more (preferably 42,000 psi or more); a diametral tensile strength ofgreater than 5,000 psi (preferably 6,000 psi or more), a hardness(Barcol) of greater than 98 (preferably 100 or more), and a linearshrinkage of 0.4% or less (preferably 0.38% or less).

While particular emphasis has been devoted herein to the use of themonomers of the present invention in composite restorative materials, itwill be understood that these monomers may also be used in other dentalmaterials. Examples of these other dental materials are given in theWaller U.S. Pat. No. 3,629,187 (Note particularly column 11, line 26 tocolumn 15, line 36) and in the Kirk-Othmer Encyclopedia of ChemicalTechnology, Third Edition, Volume 7 (1979), pages 501-508 and 515-517.Waller characterizes these materials as, e.g., dental cements, dentalcavity liners and dental lacquers. Kirk-Othmer characterizes thesematerials as, e.g., unfilled tooth-restorative resins, pit and fissuresealants and adhesives.

In addition to one or more monomers according to the present invention,dental materials may contain one or more of the copolymerizablematerials described herein, provided that such copolymerizable materialis acceptable for oral application associated with dental treatment.Particular examples of such copolymerizable material include thosemethacrylate monomers mentioned herein with respect to compositerestorative materials. The fillers described herein with respect tocomposite restorative materials may also be used in certain other dentalmaterials.

Certain dental materials may contain various amounts of filler, whileother dental materials contain no filler at all. For instance, thedental cements described in the Waller U.S. Pat. No. 3,629,187 maycontain little or no filler if a transparent cement is desired, butthese cements may contain up to about a 1:1 ratio of filler topolymerizable material if a translucent cement is acceptable. It isnoted that fillers used in dental cements generally have smallerparticle sizes (e.g., an average particle size of 10 microns or less)with respect to fillers used in composite restorative materials.

An example of a dental material containing no filler may becharacterized as a fissue sealer or as a bonding agent for use as anunder coating for a composite restorative or orthodontic adhesive. Sucha material may comprise polymerizable material comprising 65-75% byweight of at least one dimethacrylate of the present invention and35-45% by weight of a suitable diluent such as triethylene glycoltrimethacrylate. Such a material may be rapidly curable and capable ofbrush-on application. These sealers or bonding agents may cure to form asemi-translucent polymer having a Barcol hardness of 80 or more. Thebonding strength to phosphoric acid etched human enamel may be from1100-1200 psi.

An example of a dental material containing a relatively small amount offiller is an orthodontic adhesive containing as a polymerizable material50-60% by weight of the dimethacrylate of the present invention and40-50% by weight of a suitable diluent such as diethylene glycoldimethacrylate. The filler, e.g., fumed silica, may comprise 10-15% byweight of the sum of the combined weights of polymerizable material plusfiller. The bonding strength of such an adhesive to etched human enamelmay be 1200-1300 psi and the bonding strength to mesh-type orthodonticbracket bases may be 14-40 pounds depending on bracket size andindividual design of the bracket bases.

Dental materials may be cured by a photoinitiation technique using knownlight polymerization initiators or by chemically initiated systemsincluding those systems using sulfonic acid activators.

In addition to fillers and polymerizable material, dental materials maycontain other substances. For instance, pigments may be included. Also,ultraviolet absorbers or stabilizers may be included to lessendiscoloration of the cured material. Furthermore, fluorides,bacteriostatic agents and antibiotics may also be included.

Dental materials may be applied to teeth in a variety of mannersdepending upon the nature of the material and the desired use. Forinstance, thick, slow-curing materials, such as composite restoratives,may be molded and shaped in the mouth before final curing takes place.On the other hand, flowable, fast-curing materials, such as cavityliners may be simply brushed on the surface of the treated tooth.

Dental materials such as restoratives, sealers, bonding agents, cementsand orthodontic adhesives containing in their resin part 20-90% of thedimethacrylate of the present invention exhibit most desirableproperties, especially in respect to color stability, low waterabsorption, high mechanical strength and low polymerization shrinkage.

The following examples describe certain embodiments of the invention. Itis to be understood that these examples are given only to illustrate thenature of the invention and should not, in any way, be understood aslimiting the scope of this invention, defined in the claims.

EXAMPLE 1

1536 g of 1,4-bis(glycidoxymethyl)cyclohexane

1032 g of glacial methacrylic acid

6.5 g of triphenylphosphine

4.5 g of BHT

were placed in a round bottom reaction flask equipped with a condenser,heater and mechanical stirrer. The mixture was heated up to 100° C. andmaintained at this temperature while stirring until the epoxy equivalentreached a value of 0.012 or below. The excess of methacrylic acid wasthen distilled off.

The reaction product, called DECD, consists of a medium viscosity liquidhaving a refractive index n_(D) ²⁵ 1.487. 460 g of DECD was placed in around bottom flask to which 300 ml of ethyl ether was added. The etherwas then distilled off in a gentle stream of dry air in order to removeany traces of water. 170 g of butyl isocyanate was added slowly withstirring over a period of 1 hour while maintaining temperature of thereaction mixture at 45° C. This temperature and stirring was maintainedfor 10 hours after which the reaction mixture was allowed to standovernight at room temperature of 23°-27° C. The reaction productconstitutes a light yellow colored viscous liquid and represents amixture of N-butyl mono- and di- carbamates of1,4bis[(3'-methacroyl-2'-hydroxypropoxy)methyl]cyclohexane calledhereafter DECI.

EXAMPLE 2

A dental material for use as a fissure sealer or as a bonding agent tobe used under composite restorative or orthodontic adhesives has beenformulated as follows:

    ______________________________________                                        Part A                     Part B                                             (Parts by Weight)          (Parts by Weight)                                  ______________________________________                                        57          DECI           57                                                 38.5        Diethyleneglycol di-                                                                         40                                                             methacrylate                                                      0.1         BHT            0.1                                                0.4         Cyasorb UV-9   0.4                                                4.5         N,N--bis(2-hydroxy-                                                                          --                                                             ethyl)-p-toluidine                                                --          Benzoyl peroxide                                                                             2.5                                                ______________________________________                                    

Parts A and B when mixed in equal amounts cured in 120 seconds forming asemi-translucent polymer having a Barcol hardness of 80. The adhesivebond strength to phosphoric acid etched human enamel was 1100-1200 psi.Color stability in sunlight was excellent.

EXAMPLE 3

A dental composite restorative for use as a filling material in anteriorand posterior restorations has been formulated as follows:

    ______________________________________                                        Part A                      Part B                                            (Parts by Weight)           (Parts by Weight)                                 ______________________________________                                        38          DECI            38                                                26          Triethyleneglycol                                                                             26                                                            dimethacrylate                                                    31          Bis-GMA         31.9                                              0.9         Cyasorb UV-9    --                                                0.1         BHT             0.1                                               4           N,N bis(2-hydroxy-                                                                            --                                                            ethyl)-p-toluidine                                                --          Benzoyl peroxide                                                                              4                                                 500         5:1 mixture of pow-                                                                           500                                                           dered barium and boro-                                                        silicate glasses                                                              below 44 microns,                                                             treated with metha-                                                           croylpropyl trihydroxy-                                                       silane                                                            ______________________________________                                    

Parts A and B when mixed in equal amounts cured in 120 seconds. Theresulting material had the following characteristics:

    ______________________________________                                        Water Sorption at 37° C.                                                                  0.42 mg/cm.sup.2 *                                         Diametral Tensile Strength                                                                       6,000 psi                                                  Compressive Strength                                                                             42,000 psi                                                 Hardness (Barcol)  100                                                        Color Stability    Change perceptible with                                                       difficulty*                                                Opacity/translucency                                                                             0.48*                                                      factor                                                                        Linear Shrinkage   0.38%                                                      ______________________________________                                         *Determined according to American Dental Association Specification No. 27     JADA Vol. 94, June, 1977.                                                

EXAMPLE 4

An orthodontic adhesive has been formulated as follows:

    ______________________________________                                        Part A                      Part B                                            (Parts by Weight)           (Parts by Weight)                                 ______________________________________                                        44         DECI             44                                                38.4       Diethyleneglycol di-                                                                           39                                                           methacrylate                                                       .6         Cyasorb UV-9     --                                                4          N,N--bis(2-hydroxyethyl)-                                                                      --                                                           p-toluidine                                                        --         Benzoyl peroxide  4                                                13         Fumed silica     13                                                ______________________________________                                    

This adhesive cured in 60 seconds, when Parts A and B were mixed inequal amounts. Bonding strength to etched human enamel was 1200-1300 psiand bonding strength to mesh-type orthodontic bracket bases was 14-40pounds depending on bracket size and individual design of the bracketbases.

While the use of the monomers of the present invention has beendescribed primarily with respect to dental materials, particularlycomposite restorative materials, it is noted that these monomers mayalso be used in other materials such as bone cements and UV curableinks. Thus while certain representative embodiments and details havebeen shown for the purposes of illustrating the invention, it will beapparent to those skilled in the art that various changes andmodifications may be made therein without departing from the spirit orscope of the invention. It will further be understood that the inventionmay comprise, consist essentially of or consist of the steps ormaterials recited herein.

What is claimed is:
 1. A dimethacrylate of the following chemicalstructure: ##STR21## where ##STR22## is a saturated, 6 membered,monocyclic, hydrocarbyl ring system; R₁, R₂ and R₃ are the same ordifferent and are hydrogen or alkyl or alkoxy groups having 1 to 12carbon atoms; andR₄ and R₅ are the same or different and are hydrogen orgroups of the formula: ##STR23## where R₆ is an aliphatic, aromatic orcycloaliphatic group having 1 to 14 carbon atoms, provided that at leastone of the groups R₄ and R₅ is a group of the formula: ##STR24##
 2. Adimethacrylate according to claim 1 wherein R₁, R₂ and R₃ have 1 to 4carbon atoms.
 3. A dimethacrylate according to claim 1 wherein R₁, R₂and R₃ are each hydrogen.
 4. A dimethacrylate according to claim 1 whereR₆ is a hydrocarbon or haloaryl group.
 5. A dimethacrylate according toclaim 4 wherein R₁, R₂, and R₃ are hydrogen or alkyl of 1 to 4 carbonatoms.
 6. A dimethacrylate according to claim 5 wherein R₆ is ahydrocarbon group.
 7. A dimethacrylate according to claim 6 wherein R₆is alkyl.
 8. A dimethacrylate according to claim 7 wherein R₁, R₂, andR₃ are all hydrogen.
 9. A dimethacrylate according to claim 8 wherein R₄is hydrogen or ##STR25## and R₅ is ##STR26##
 10. A dimethacrylateaccording to claim 9 where R₄ is hydrogen.
 11. A dimethacrylateaccording to claim 9 where R₄ is ##STR27##
 12. A composite restorativematerial according to claim 1, wherein:(i) said at least one firstmonomer and said at least one third monomer each constitute from about30% to about 50% by weight of said polymerizable material, provided thatthe total amount of said at least one first monomer plus said at leastone third monomer constitutes from about 70% to about 80% by weight ofsaid polymerizable material; (ii) said at least one second monomerconstitutes from about 20% to about 30% by weight of said polymerizablematerial; and (iii) said ratio of said filler to said polymerizablematerial is from about 4:1 to about 6:1.